1. Technical Field
The present invention relates to an optical article having a functional thin film (functional layer), such as an anti-reflection layer, which is formed on an optical substrate made of glass or plastic, and a manufacturing method of the optical article.
2. Related Art
In a process of manufacturing various kinds of optical articles, various kinds of functional thin films (functional layers), including a hard coat layer, a colored layer, an anti-reflection layer, an anti-smudge layer, etc., are formed on an optical substrate made of glass or resin, directly or with a primer layer interposed therebetween. In addition, in a process of manufacturing a spectacle lens or other optical articles, an anti-reflection layer is formed on an optical substrate made of glass or resin, directly, or with a hard coat layer interposed therebetween, or with a primer layer and a hard coat layer interposed therebetween, in order to suppress reflection of light and increase transmittance of light. As one type of the anti-reflection layer, there is an anti-reflection layer having a multi-layered structure where a sub-layer having a low refractive index and a sub-layer having a high refractive index are stacked. The sub-layer having the low refractive index is preferably made of silicon oxide such as SiO2, SiOx or the like, or MgF2. The sub-layer having the high refractive index is preferably made of ZrO2, Ta2O5, TiO2, CeO2, Y2O3 or the like. A sub-layer having a medium refractive index and made of Al2O3, CeF3 or the like may be employed for the anti-reflection layer.
For formation of the functional thin film or the anti-reflection having the multi-layered structure, a vacuum deposition method is widely being used, which stacks material composing a thin film or material composing a sub-layer on an optical substrate by heating and evaporating the material in vacuum by means of an electron gun, resistance heat or the like.
P-A-2005-187936 discloses a film forming apparatus having three chambers, a third chamber of which being used to form an anti-smudge layer on an anti-reflection layer. In operation of this apparatus, after an optical substrate is put in a first chamber, the anti-reflection layer is deposited on the optical substrate in a second chamber, and then, an anti-smudge layer is formed on the anti-reflection layer in the third chamber.
It is important to improve durability, particularly, scratch resistance, of an anti-reflection layer having a multi-layered structure in order to keep a surface state, which has an great effect on an optical characteristic of an optical article, in good condition. It is known that a semiconductor optical part such as an image sensor is formed of a silicon nitride thin film having high durability and high transparency.
JP-A-5-214515 discloses a technique in which a silicon nitride thin film is formed on a substrate by depositing silicon on the substrate in vacuum and irradiating nitride ions on the deposited silicon. A silicon nitride layer has excellent transparency. For this reason, it is possible to employ the silicon nitride layer as a sub-layer of an anti-reflection layer having a multi-layered structure. For the anti-reflection layer, a homogeneous layer needs to be formed at a predetermined thickness in order to attain a desired optical effect. However, it is difficult to form the silicon nitride layer stably. In addition, the technique disclosed in JP-A-5-214515 requires precise control for deposition speed of silicon and the amount of irradiation of nitride ions.
In addition, an anti-reflection layer including a layer having a low refractive index and a layer having a high refractive index according to the above-described composition has been some designed to attain an optical system having high transparency. However, in this anti-reflection layer, a silicon nitride layer has a refractive index different from the layer having the above-described composition. Although the silicon nitride layer basically has a high refractive index, since it is different in refractive index different from other layers having a high refractive index, there is a need to design a new optical system.
In addition, when a silicon nitride layer is employed as a layer having a high refractive index, an interface between the silicon nitride layer and a silicon dioxide layer employed as a layer having a low refractive index is expected to have a composition of SiONx. It is difficult to control a refractive index and a film thickness of a layer including the interface. For example, although a Si3N4 layer has a high refractive index of about 2.05, the refractive index falls within a range of 1.45 to 2.05 if a SiNxOy layer and a SiO2 layer are mixed with the Si3N4 layer. It is expected that durability of an anti-reflection layer formed of a silicon nitride sub-layer and a silicon dioxide sub-layer significantly increases. However, it is difficult to manufacture an anti-reflection layer having a sufficiently excellent optical characteristic.
In addition, it is important to provide a functional thin film having high durability, particularly, high scratch resistance in order to keep a surface state, which has an great effect on an optical characteristic of an optical article, in good condition. It is known that a semiconductor optical part such as an image sensor is formed of a silicon nitride thin film having high durability and high transparency.
In general, a silicon dioxide thin film is formed alone or as a portion of a multi layer on an optical substrate. In particular, if the optical substrate is made of resin, durability of the optical substrate depends on scratch resistance of the silicon dioxide thin film.
A silicon nitride thin film has improved scratch resistance over the silicon dioxide thin film. JP-A-5-214515 discloses a technique in which a silicon nitride thin film is formed on a substrate by depositing silicon on the substrate in vacuum and irradiating nitride ions on the deposited silicon. However, it is difficult to form the silicon nitride layer stably. The technique disclosed in JP-A-5-214515 requires precise control for deposition speed of silicon and the amount of irradiation of nitride ions.